直径
The distance from one side of a circle to the other, passing through the center point. It is a fundamental measurement used in geometry and daily life to describe the size of round objects like plates or pipes.
Examples
3 of 5このピザの直径は30センチです。
The diameter of this pizza is 30 centimeters.
太陽の直径は、地球の約109倍です。
The diameter of the sun is approximately 109 times that of the Earth.
ねえ、このボールの直径ってどれくらい?
Hey, what is the diameter of this ball?
Word Family
Memory Tip
The first kanji 直 (choku) means 'straight.' Think of a 'straight' line passing directly through the middle of a circle.
Quick Quiz
円の___は、半径の2倍の長さです。
Correct!
The correct answer is: 直径
Examples
このピザの直径は30センチです。
everydayThe diameter of this pizza is 30 centimeters.
太陽の直径は、地球の約109倍です。
formalThe diameter of the sun is approximately 109 times that of the Earth.
ねえ、このボールの直径ってどれくらい?
informalHey, what is the diameter of this ball?
円の面積を計算するには、直径ではなく半径が必要です。
academicTo calculate the area of a circle, you need the radius, not the diameter.
このパイプの直径は、規格に合わせて50ミリにしてください。
businessPlease ensure the diameter of this pipe is 50mm according to the standards.
Word Family
Common Collocations
Common Phrases
直径に等しい
equal to the diameter
内径と外径
inner diameter and outer diameter
直径の長さ
the length of the diameter
Often Confused With
Hankei (radius) is half the distance of the diameter (chokkei).
Enshū (circumference) is the distance around the circle, not across it.
Usage Notes
While commonly used in math, it is also frequently used when buying household items like frying pans, pots, or lightbulbs.
Common Mistakes
Learners often confuse 'chokkei' (diameter) with 'hankei' (radius). Also, avoid using 'nagasa' (length) alone when the specific dimension needed is the diameter of a circle.
Memory Tip
The first kanji 直 (choku) means 'straight.' Think of a 'straight' line passing directly through the middle of a circle.
Word Origin
From the kanji 直 (direct/straight) and 径 (path/diameter). It literally means the 'straight path' through a circle.
Grammar Patterns
Cultural Context
In Japan, many household goods are categorized by diameter using the unit 'cm' or 'mm', which is essential for home shopping.
Quick Quiz
円の___は、半径の2倍の長さです。
Correct!
The correct answer is: 直径
Related Vocabulary
Related Words
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